A typical manual powertrain is illustrated in FIG. 1. Solid lines represent mechanical power flow through rotating shafts. Dashed lines represent control connections, which may be implemented using mechanical linkages. Engine 10 generates power at crankshaft 12 by burning fuel. The engine responds to changes in the position of accelerator pedal 14 to generate more power when the pedal is depressed further by the driver. Transmission 16 transmits power from crankshaft 12 to output shaft 18. Transmission 16 includes a friction clutch 20 and a gearbox 22 connected by input shaft 24. Gearbox 22 is capable of establishing a variety of forward speed ratios and at least one reverse speed ratio in response to driver manipulation of shifter 26. The driver controls the torque capacity of clutch 20 by manipulation of clutch pedal 28. Conventionally, the torque capacity of clutch 20 is negligible when clutch pedal 28 is fully depressed and is at a maximum when clutch pedal 28 is fully released. Differential 30 splits power from output shaft 18 between a left half-shaft 32 driving a left wheel 34 and a right half-shaft 36 driving a right wheel 38 while permitting slight speed differences between the wheels as the vehicle turns a corner. In a typical rear wheel drive powertrain, the transmission output shaft is a driveshaft that extends to the differential. In a typical front wheel drive powertrain, the output shaft 16 may be driveably connected to the differential by a final drive gear. The transmission and differential of a front wheel drive powertrain are frequently combined into a single housing and called a transaxle.
For internal combustion engine 10 to generate power, crankshaft 12 must rotate at sufficient speed. However, when the vehicle is stationary with gearbox 22 establishing a speed ratio, input shaft 24 is also stationary. In order to start the vehicle moving, the driver controls the torque capacity of clutch 20 to transmit power from moving crankshaft 12 to stationary input shaft 24. As the vehicle accelerates, the speed of input shaft 24 gradually increases until it is equal to the speed of crankshaft 12, at which point clutch 20 can be fully engaged. With clutch 20 fully engaged, the speed of crankshaft 12 is proportional to vehicle speed. As the vehicle accelerates in 1st gear, the speed of crankshaft 12 becomes excessive, necessitating a shift to 2nd gear. Similarly, upshifts are required when the crankshaft speed becomes excessive in any of the other gears. Downshifts are required whenever the crankshaft speed becomes too low. Gearbox 22 is not capable of changing ratios while transmitting power. Therefore, the driver shifts by disengaging clutch 20, then manipulating shifter 26 to change the gearbox ratio, then re-engaging clutch 20. Re-engagement of clutch 20 forces the crankshaft speed to become equal to input shaft speed, predominantly by changing the speed of the crankshaft.
During a launch event, the driver must coordinate the movement of clutch pedal 28 and accelerator pedal 14. The acceleration rate during a launch is proportional to the clutch torque capacity. To launch with a desired acceleration rate, the driver must position the clutch pedal to the position corresponding to the desired clutch torque capacity. If the pedal is depressed too far, the clutch torque capacity is less than desired and the vehicle accelerates too slowly, and may even roll backwards if it is facing uphill. If the clutch pedal is not depressed far enough, the torque capacity is higher than desired resulting in more vehicle acceleration than desired. If the accelerator pedal 14 is pressed too much relative to the actual depression of clutch pedal 28, the engine will accelerate. If this goes unchecked, the engine speed will become excessive, resulting in a drawn out launch event with excessive energy dissipation in the clutch. If accelerator pedal is not depressed far enough relative to the actual depression of clutch pedal 28, the engine speed will decrease which can result in an engine stall.
Many new drivers of manual transmissions have difficulty manipulating the clutch pedal and accelerator pedal properly during a vehicle launch. Similarly, drivers with poor hearing may have difficulty due to the lack of audible feedback regarding engine noise. This difficulty is exacerbated by the non-linear relationship between clutch pedal position and torque capacity. As the driver releases the clutch pedal from a fully depressed position, the torque capacity remains at near zero until the pedal reaches a point called the touch point. Then, as the driver further releases the pedal, the torque capacity increases reaching full capacity before the clutch pedal is fully released. New drivers often have difficulty finding the touch point. If the driver errs on the side of depressing the pedal too far, then the vehicle does not accelerate and the engine may race due to the engine torque exceeding the clutch torque capacity. If the driver errs on the side of releasing the pedal too far, the torque capacity is excessive causing a jerky launch or stalling the engine.
Furthermore, the pedals must also be coordinated when completing a gear shift. To re-establish positive torque after a gear shift, the crankshaft speed should slightly exceed the input shaft speed when the clutch pedal is released. After a downshift, the driver must increase the crankshaft speed using the accelerator pedal. After a downshift, the engine speed will decrease on its own, but may decrease to less than the input shaft speed if the gear shift takes too long. If the clutch is released when the crankshaft speed is less than the input shaft speed, the torque will be negative, causing the vehicle to decelerate. If the crankshaft speed exceeds the input shaft speed by too much, the re-engagement will likely be jerky.